Forum Schedule Spring 2021
All talks are conducted online
Fridays 3:45pm - 4:45pm BPB-217
| Date | Speaker | Topic (click down-arrow to see abstract) | |
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| Jan 22 |
Jason Barnes University of Idaho, Moscow host: David Jeffery Meeting link: https://unlv.webex.com/unlv/j.php?MTID=ma94ba6b10c8f8361c2302f4fc9335539Meeting number: 120 184 5016Password: 3kAfTBT3c$3
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Dragonfly: NASA's Titan Rotorcraft Lander | |
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Dragonfly is NASA's most recently selected planetary mission. Its science is prebiotic chemistry, habitability, and a search for chemical biosignatures on Saturn's huge moon Titan. Titan's draw derives from its status as an Ocean World. Like Europa, Enceladus, and potentially other icy outer solar system objects, Titan sports a liquid water ocean beneath its icy outer crust. But unlike those sister Ocean Worlds, Titan's surface and atmosphere contain a large quantity and complexity of carbon compounds. When liquid water develops transiently on Titan's surface -- either from cryovolcanism or impact melt -- water mixes with that surface organic material. Dragonfly will explore the chemistry of the resulting mixture at 80-km-diameter Selk Crater where that water, though now frozen, shows pathways for prebiotic chemistry that may resemble the process through which life formed on Earth 4 billion years ago. In my colloquium, I will discuss the specific scientific experiments that the Dragonfly lander will enable, as well as the instrumentation and exploration strategies that the science team will use to answer our science questions once we land in the mid-2030s. |
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| Jan 29 | |||
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| Feb 12 |
Akimasa Kataoka National Observatory of Japan (NAOJ) host: Chao-Chin Yang |
Measuring the grain size in protoplanetary disks by ALMA polarization observations | |
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Dust coagulation is the first stage of planet formation, and observational constraints on the grain size in protoplanetary disks are essential for unveiling planet formation. We are tackling this task by using ALMA polarimetric observations. While polarization has been used for finding the direction of magnetic fields, we have shown that this is not the case in protoplanetary disks; the major process of the polarization is due to self-scattering of thermal dust emission. This new mechanism reveals that dust grains have a size of ~100 micron in protoplanetary disks. This contradicts a common assumption of millimeter to centimeter grains inferred from spectral index measurements. In this talk, I would like to discuss the basic mechanisms of the self-scattering polarization and implications to planet formation through the grain size measurements.
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| Feb 19 | |||
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| Feb 26 | |||
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| Mar 5 | |||
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| Mar 12 | |||
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| Mar 19 | Spring Break | ||
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| Mar 26 | |||
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| Apr 2 |
Beibei Liu Zhejiang University, China host: Chao-Chin Yang |
From pebbles to planets | |
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Four major stages of planet formation are introduced through the talk. Dust grains first coagulate by perfect sticking but they cannot further grow much beyond cm size. Streaming instability is a key mechanism that clusters pebbles (~mm–cm size particles) into planetesimals with the help of self-gravity. After planetesimals form, they can grow into protoplanets by feeding from other planetesimals as well as by accreting inwardly drifting pebbles from the outer disk. The transition from planetesimal-dominated accretion to pebble-dominated accretion is around 1E-2 Earth mass. The subsequent planet growth is driven by pebble accretion and their core masses are regulated by the pebble isolation mass. I will present a pebble-driven core accretion model to study the formation of planets around low-mass stars and brow dwarfs. The forming planets are compared with the observed exoplanets in terms of mass, metallicity and water content. The results succeed in quantitatively reproducing several observed properties of exoplanets and correlations with their stellar hosts.
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| Apr 9 | |||
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| Apr 16 |
Patrick Mullen University of Illinois Urbana-Champaign host:Daniel Proga |
Magnetized Models for the Formation of the Moon | |
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The leading theory for the origin of the Moon suggests that a planetary impactor struck the proto-Earth in an oblique collision shortly after the formation of the solar system. The giant impact produces liquid and vapor debris, drawn from the proto-Earth and impactor. The debris either escapes the system, falls back to the Earth, or enters circumterrestrial orbits forming a "protolunar disk". In this talk, I will highlight a suite of numerical models, using the Athena++ astrophysical magnetohydrodynamics framework, that investigates the dynamical role of magnetic fields in a Moon-forming giant impact scenario. Our models demonstrate that magnetic fields speed the evolution of the vapor component of the protolunar disk, while making Moon formation less efficient.
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| Apr 23 | |||
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| Apr 30 | |||
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| May 7 |
Woojin Kwon Seoul National University, Korea host: Chao-Chin Yang |
Magnetic Fields of Star Formation Revealed on the Intermediate and Small Scales | |
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Magnetic fields affect star formation in a broad range of scales, from parsec to hundreds au scales. In this talk, I will present our recent studies on magnetic fields in star forming regions and young stellar objects (YSOs) on intermediate (1000–10000 au) and small (~100 au) scales. For the intermediate-scale magnetic fields, I will introduce the B-fields In STar forming Region Observations (BISTRO) project, which is a large program of the James Clerk Maxwell Telescope, focusing on the results toward the Serpens Main molecular cloud. Particularly, orientations of magnetic fields with respect to structures will be discussed. For the small scales, I will discuss the effects of magnetic fields on early disk formation. Previously, when magnetic fields are aligned to the bipolar outflow of a YSO, it is not expected to form a disk at the early stage, due to catastrophic magnetic braking. However, our recent ALMA observations toward L1448 IRS 2, which has a rotation detected and its magnetic fields aligned to the bipolar outflow (poloidal fields) on ~1000 au scales, show that the fields switch to toroidal at the center on ~100 au scales. This result suggests that magnetic braking may not be so catastrophic for early disk formation even in YSOs with magnetic fields aligned to the bipolar outflow.
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| May 14 | Finals Week | ||
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Past forums: Fall 2020 Spring 2020 Fall 2019 Spring 2019 Fall 2018 Spring 2018 Fall 2017 Spring 2017 Fall 2016 Spring 2016 Fall 2015 Spring 2015 Fall '14 Spring '14 Fall '13 Spring '13 Fall '12 Spring '12 Fall '11 Spring '11 Fall '10 Spring '10 Fall '09 Spring '09 Fall '08